The process of vaccinating eggs is important in the medical field and in poultry production. In medicine, eggs are used to incubate biological material utilized in the production of vaccines. In poultry production, the objective of in-egg vaccination is to protect the animals from endemic diseases.
Embryos receiving vaccine three days before hatching instead of the first day after hatching have more time to develop antibodies and consequently have a greater resistance to diseases. In this process, the vaccine ideally is applied directly into the allantoidal cavity of the egg, without direct needle contact with the embryo.
The incubation time for a chicken embryo is typically 21 days and in-egg vaccination is normally performed three days prior to hatching during the routine process of transferring the eggs from the incubator machine to the hatcher machine. The eggs that have previously been secured in incubator trays in which the eggs are fixed in a vertical position are now transferred in sets of one to four flats into hatcher baskets where they are allowed to lay down in unencumbered positions so that they can hatch without injury.
The structure of the egg is composed of a shell, a membrane adhering to the inside of the shell, and an interior membrane holding the embryo within the allantoidal fluid.
When the egg is laid, the two membranes are in contact with one another, but they gradually separate during the incubation process, creating an air cell between the membranes. This air cell is located in the top of the egg as per its position in the incubator tray.
The process of vaccinating in-egg must be done with care to avoid cracking the egg shell or penetrating the embryo, either of which can be fatal to the embryo
The vaccinator described in previous U.S. Pat. No. 6,240,877, issued to Bounds, has a rolling bridge which supports the vaccinating platform and transports it through the vaccination positions and then moves it to the sanitization chamber where the needles and injectors are sprayed with a disinfecting spray. The vaccinating platform has sufficient needles for vaccinating only one tray, usually meaning one third or one fourth of the total eggs that will be transferred, so 3 or 4 cycles of injections are needed to vaccinate all of the eggs for a conventional hatcher tray.
This means that each needle is used to vaccinate three or four eggs before being sanitized. The vaccination of more than one egg without sanitization creates the potential for spreading contamination from one egg to the next during the cycle. The repetitiveness of the vaccination cycle results in a slow process and low productivity.
The in-egg vaccinator referred to in the Bounds patent has an injector platform made of three plates, two metal plates and one fiberglass plate that support and guide the vaccine injectors. The plates have identical holes that are slightly larger than the diameter of the injectors and only permit the injectors to move vertically. There is no lateral movement to accommodate eggs that are seated in the incubator tray at an angle to the vertical position.
Once the set of incubator trays has been positioned below the injector platform, the platform is lowered over the eggs and the injectors are positioned so that they sit on top of the eggs. The platform continues to be lowered until it reaches the end of its stroke or course. The middle plate of the platform is pushed slightly to one side by an air cylinder to lock the injectors in their vertical positions. If the eggs are slightly tilted, the needle then enters the shell at an angle that may cause the shell to crack and may make contact with the embryo, both of which can be fatal to the embryo.
The injector used for vaccination has a metal pneumatic air cylinder encased in a plastic sleeve. The air cylinder has a hollow plunger through which the needle passes. A return spring inside the air cylinder causes the needle to return to its initial position after it has injected the egg.
One of the major drawbacks of the injector referred to above is that the metal air cylinder suffers severe oxidation resulting from the strong corrosive action of the disinfectants used to sanitize the vaccinator. The build up of oxidized material on the plunger inhibits its movement and eventually freezes it in place. The repair and substitution of the air cylinder causes production delays in addition to higher costs.
The referred to model of vaccinator in the above patent requires 100 psi of air pressure in order for the needle to penetrate the egg shell without cracking the shell. After passing through the shell, the needle passes through the air cell at the same pressure, penetrates the allantoidal membrane, and continues until it reaches its course length, and vaccine is injected into the allantoidal liquid which is absorbed by the embryo.
Because of the high pressure with which the needle must break the shell, the above referenced process requires the use of different length needles, varying from 22 cm to 25 cm depending on the size of the egg, which is determined by the age of the laying flock. An egg from a flock of older parent birds will have an air cell larger than an egg from a younger parent bird and if a long needle is used to vaccinate an egg from a young flock there is a high probability that the embryo will be punctured by the needle causing injury or death. Even if the appropriate needle length for the flock age is used, it frequently happens that the embryo is positioned higher in the egg and is hit by the needle under high pressure, thereby causing death to the embryo. In addition to the monetary loss from embryo death, the need for various sized needles reduces the hatchery productivity.
The vaccinator referred to above injects vaccine through every injector regardless of whether or not an egg is in position below the injector. Hatching eggs can have up to 15% or more infertile eggs that will not hatch. A common practice is to remove the infertile eggs in a process called candling, a few days before transfer. The injection into the space without an egg is an expensive waste of vaccine.
The sanitization system of the vaccinator referred to above is one additional process which occurs after the vaccinator has injected a series of incubator trays. The rolling bridge moves the vaccination platform beyond the injection area and into the sanitization chamber where the injector platform and needles are sprayed with sanitation products. After sanitization has been completed, the injector platform is returned to the position over the next eggs to be injected.
The vaccinator referred to above is manufactured to inject only one size of incubator tray. Many hatcheries have more that one size tray, requiring that the hatchery have two or more in-egg vaccinators to vaccinate all of its eggs.